SeO 2 adsorption mechanisms on CaO surface were firstly investigated by both density functional theory (DFT) calculations and adsorption experiments. Adsorption of multiple SeO 2 on the CaO (001) surface was investigated using slab model. Based on the results of adsorption energy and surface property, a double-layer adsorption mechanisms were proposed. In experiments, the SeO 2 adsorption products were prepared in a U-shaped quartz reactor at 200 °C. The surface morphology was investigated by field emission scanning electron microscopy (FE-SEM). The superficial and total SeO 2 mass fractions were measured by X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma atomic emission spectroscopy (ICP-AES), respectively. The surface valence state and bulk structure are determined by XPS and X-Ray Diffraction (XRD). The experimental results are in good agreement with the DFT results. In conclusion, the fundamental SeO 2 chemisorption mechanisms on CaO surface were suggested.
The calcium looping is a promising technology to achieve industrial CO 2 capture, and the introduction of oxygen vacancy can promote the CO 2 capture reactivity of CaO-based sorbents. In this work, DFT calculations were performed to investigate the CO 2 adsorption by CaO in the presence of oxygen vacancy defect. The presence of oxygen vacancy reduces the band gap of CaO surface, which results from the delocalization of Ca 2p orbital. Besides, the electron accumulation at the oxygen vacancy occurs due to the unsaturated Ca-O bonds, and the reaction possibility is promoted neighbouring the defect. The top site of oxygen vacancy defect of CaO is favourable for CO 2 adsorption. The adsorption energy of CO 2 on CaO with oxygen vacancy achieves − 2.52 eV, which is 1.81 times as high as that on pristine CaO. Due to strong interaction between CO 2 and CaO with oxygen vacancy, CO 2 migration from this site is more difficult, while the following diffusion is more prone to occur. In the presence of steam, CO 2 adsorption energy is enhanced to − 2.70 eV on CaO with oxygen vacancy, and the distance from CO 2 radical to surface is intuitively reduced, which results from the electrons donated from defect and neighbouring Ca atoms, while CO 2 diffusion difficulty is increased. This work provides an incisive investigation for structural, electronic, and thermodynamic characteristics of CO 2 adsorption and diffusion on CaO in the presence of oxygen vacancy defect, and it can shed light on rational synthesis and functional design of surface-active sites of CaO-based sorbents.
Xianyao Yan,Yingjie Li,Chunxiao Zhang,Yuzhuo Wang,Jianli Zhao,Zeyan Wang
The water gas shift reaction is an important reaction for H 2 production in various industrial applications. The presence of CaO can promote the reactivity of the water gas shift reaction without any catalysts, but the enhancement mechanism of CaO in this reaction is difficult to determine just by the experiment. In this work, the water gas shift reaction along four possible pathways on the CaO surface were studied by density functional theory (DFT) analysis. The energy barriers along the pathways were analyzed to determine the most possible reaction pathway and role of the CaO surface. The DFT calculation results show that the WGS reaction is more prone to proceed along the redox-a pathway probably: H 2 O dissociates into hydroxyl and atomic H spontaneously when H 2 O and CO co-adsorb on the CaO surface, then the hydroxyl continues to dissociate and CO is oxidized by the generated atomic O. Afterwards, H 2 molecule generates from two atomic H, and then CO 2 adsorbs and H 2 desorbs simultaneously on the CaO surface. The CaO surface enables the spontaneous dissociation of H 2 O, which is the rate-limiting step of WGS reaction. The generation of CO 2 is facilitated, and the energy barrier is reduced from 2.304 to 0.757 eV on the CaO surface. Besides, the formation of CO 3 2− on the surface avoids the energy barrier for CO 2 desorption, while the CO 2 also occupies the active site and reduces the enhancement of CaO on WGS reaction. The calculation result reinforces the comprehension on the mechanism of CaO on WGS reaction.
危险品化学品经营许可证（带存储）